The present invention relates generally to integrated circuit designs, and more particularly to an electrical fuse device with dummy cells for electrostatic discharge (ESD) protection.
Electrical fuse devices are designed for storing data on a one-time programming basis. An electrical fuse cell typically includes an electrical fuse and a switch device, such as an NMOS (N-channel metal-oxide-semiconductor) transistor. The electrical fuse can be selectively programmed to demonstrate a high or low resistance level for representing a logic value. If the fuse is programmed, its resistance will permanently increase. Thus, the electrical fuse device is often referred to as a one-time programming memory device.
The electrical fuse device is particularly susceptible to the influence of an ESD current because of its one-time programming nature. The ESD current can easily reach a voltage level of thousands of volts. When the ESD current enters the electrical fuse device, it can blow many of the electrical fuses. Since the electrical fuse has a one-time programming nature, its resistance will not bounce back after the ESD current dissipates, thereby causing irreparable data errors.
Conventionally, an RC-delay or DC circuit is implemented in the electrical fuse device for turning off the switch device in order to prevent the ESD current from flowing through the electrical fuse during an ESD event. However, the conventional ESD protection mechanism may have certain drawbacks. When an ESD occurs, the ESD current always needs to find a less resistive dissipation path. While the conventional ESD protection mechanism may turn off some current paths, the ESD current may still flow through other less resistive path and cause damages. It is very difficult to predict the ESD current path and design a protection mechanism accordingly. In some cases, the ESD voltage is so high that a punch-through may occur across a switch device that is turned off by the protection mechanism during the ESD event.
As such, what is needed is an electrical fuse device with improved ESD protection designs.